The broad objective of this research is to investigate T cell responses to self and nonself immunoglobulins. The fact that IgG2a antigens are naturally expressed in Ia B lymphoma cells known to be fully capable of antigen presentation and that the structure of the antigen is readily manipulated using recombinant DNA techniques gives this system unique advantages for studying possible relationships between complex intracellular trafficking pathways and MHC restriction specificity. We plan to construct pSV2gt vectors encoding various forms of the C57BL/6 IgG2ab CH3. We are particularly interested in this portion of the molecule because allotypic determinants recognized by Igh-1b-specific T cell are located in the CH3 domain. Soluble, membrane-bound,and cytoplasmic form(s) of the C57BL/6 IgG2ab CH3 will be expressed in transfected B lymphoma cell lines. We will characterize the protein products that are synthesized and test whether these molecules are presented to Class II-restricted T cells. A major goal is to determine whether endogenously synthesized IgG2a antigens become associated with Class II molecules intracellularly. We will also express the VMPC11 -C57BL/6 IgG2ab CH3 protein under control of the human B- actin promoter in a variety of different types of Ia+ APC lines to test whether endogenous IgG2a synthesized by different types of Ia+ APC will stimulate Igh-1b-specific T cells. Overall, these experiments will hopefully lead to a clearer understanding of the possible role of antigen-presenting cells in MHC-restricted T cell recognition of self immunoglobulins and processes involved in T cell tolerance.